Method and system for mechanical separation of various materials/substances from disposed fluorescent light tubes and similar lamps being crushed

ABSTRACT

Method and system for mechanical separation of materials from discarded fluorescent light tubes being broken up. The system comprises a fan-driven exhaust air system which is designed for air transportation and separation of material fragments and which is supplied with air from three separating towers (8, 8&#39;, 8&#34;). A mill (2) which breaks up the fluorescent light tubes delivers fluorescent light tube material to a first separating tower (8) where larger material fragments are separated off, while smaller material fragments and particles leave the tower together with the outflowing air. A screen (22) divides the coarse fraction from the tower into glass fragments and metal fragments. The metal fragments from the screen are made to pass through a metal crusher (28) which is connected to a second separating tower (8&#39;). A magnetic separator (34) separates off magnetic material from a conveyor (32) for the glass fragments and metal fragments. From the conveyor (32), the glass fragments are made to pass through a glass crusher (42) which is connected to a third separating tower (8&#34;). From the coarse fraction outlet of the third tower, the glass fragments are conveyed via a tumbler to a waste container (54). A cyclone (58) with downstream filters (66, 70) separates off fluorescent powder from the exhaust air.

FIELD OF THE INVENTION

The present invention concerns both a method and a system for mechanicalseparation of various materials/substances from discarded fluorescentlight tubes and similar low-pressure discharge lamps being broken up.

BACKGROUND OF THE INVENTION

A fluorescent light tube is a type of low-pressure discharge lamp whichin most cases is designed as a closed glass tube (which, for example,can be straight, circular, or bent in a U-shape) with a cathode at eachend. The glass tube encloses a gas filling containing mercury vapour.When the fluorescent light tube is switched on, an electron currentpasses through the gas filling from one cathode to the other. Mercuryatoms in this gas filling are then acted upon by the electron current insuch a way that they emit invisible ultraviolet radiation. On the innerside of the glass tube there is a layer of fluorescent powder(fluorescent substance) which has the property of converting theshort-wave ultraviolet radiation into long-wave visible light.

Since a fluorescent light tube therefore contains a certain (albeitsmall) quantity of mercury, it is extremely important, from theconventional point of view, when disposing of used fluorescent lighttubes, to deal with the mercury from these tubes in an efficient andsafe manner. Discarded fluorescent light tubes must therefore be treatedas exceptional hazardous waste which is sent to a special destructionplant where the mercury can be dealt with and recovered in a mannerwhich is efficient and, from the point of view of environmentalprotection, completely satisfactory.

In a fluorescent light tube which is to be disposed of, the mercurywhich has condensed from the mercury vapour is found on the inner sideof the glass tube wall, and since this inner side is coated with afluorescent powder layer, most of the condensed mercury is thereforefound in the fluorescent powder.

Additional mercury, in the form of mercury oxide and/or amalgam, is alsofound as precipitated particles which have deposited on the inner sideof the glass tube wall, especially in the vicinity of the cathodes atthe ends of the fluorescent light tube.

Analysis of various parts of crushed or ground fluorescent light tubeshas additionally shown that the so-called cathode screen (usually aferrous strip bent round the cathode) can itself have a relatively highconcentration of mercury, for which reason it should be the subject ofspecial treatment for separating off mercury, for example distillation.

A number of methods are already known for dealing with themercury-containing fluorescent powder from discarded fluorescent lighttubes. In one of these known procedures, the cathodes and the endsections including the metal end-sleeves (the end sockets provided withcontact pins) of the fluorescent light tube are cut loose or cut offfrom the rest of the tube so that the latter is open at its ends. Thefluorescent powder can then be suctioned or raked out of the tube withthe aid of some suitable type of plunger-like scraper tool which has along shaft and which is pulled or pushed through the glass tube, open atits ends, from one end to the other end.

While it is true that most of the mercury-containing fluorescent powdercan in this way be cleared out of the glass tube cut off at its ends,the mercury-containing fluorescent powder and the mercury oxide found inthe cut-off end sections of the fluorescent light tube cannot be dealtwith and recovered in this way. The cut-off end sections can of coursethemselves be after-treated and distilled.

When the destruction of discarded fluorescent light tubes involves thefluorescent light tubes being crushed in their entirety (for example ina screw feeder), this also has the consequence that the lead oxide glasswhich is used as the end seals of the glass tube and as cathode holderswill be mixed with the crown glass from the remaining parts of thefluorescent light tubes. This is a considerable disadvantage since itmeans that the usability of the recovered glass as a raw material forthe manufacture of new glass products is thereby limited. The value ofthe recovered glass as a recovered raw material for the manufacture ofnew glass products is in this way drastically reduced.

In EP-A-0420367 there is disclosed a method and device for sanitation ofmercury-containing lamps. DE-A-4030732 discloses a method for recyclingof fluorescent lamps/tubes and broken pieces thereof. WO-A-9301889discloses a method for removing metal electrical tips from fracturedglass derived from a fluorescent tube crusher, and a tip separator foruse with crushed fluorescent light tubes.

OBJECTS OF THE INVENTION

An aim of the invention is to make available a novel method and systemfor mechanical separation of various materials/substances, and inparticular all the mercury, from all parts of a discarded fluorescentlight tube being broken up.

More specifically, an aim of the invention is to make available amechanical treatment and separation of fluorescent light tubes in such away that the component parts of the fluorescent light tubes are, inquite general terms, separated and divided up into three fractions,namely magnetic end-sleeve material (end socket material), fragments andmercury-containing fluorescent powder. As regards the glass which isrecovered, it is particularly desirable to ensure that lead glass fromthe end-sleeve is not mixed with the crown glass from the remainder ofthe fluorescent light tubes.

SUMMARY OF THE INVENTION

The abovementioned aims are achieved, according to the invention, byvirtue of the fact that the method involves the steps recited in themethod claims while the corresponding system, which can be used forcarrying out the method, has the structural elements specified in thesystems claims.

According to the method of the invention, discarded fluorescent lighttubes are fed into a mill (preferably a hammer mill) where they arebroken up into fairly large pieces or material fragments. With the aidof a current of air moving at a relatively high speed (for example 20m/s), the material fragments are then transported from the mill and inthrough the inlet into a first separating tower where larger materialfragments, of glass and metal, are separated off from the current of airand are discharged from the tower (preferably through a coarse fractionoutlet at the bottom end of the tower), while smaller material fragmentsand particles, such as fluorescent powder, are conveyed by the currentof air onwards out through the air outlet of the tower, which air outletfunctions as a fine fraction outlet.

The larger material fragments discharged from the tower are then dividedup into glass fragments and metal fragments by screening/sieving, andthe glass fragments are conveyed onwards past a magnetic separator,while the metal fragments are fed into a crusher, where they arecrushed, and are then introduced by means of a current of air throughthe inlet into a second separating tower. The metal fragments dischargedfrom the coarse fraction outlet of this second tower are then alsoconveyed past the magnetic separator. The magnetic material fragmentsseparated off by means of this separator are thereafter collected in avessel for possible further treatment, for example distillation.

The glass fragments which have passed the magnetic separator are thenfed into a glass crusher where they undergo a further reduction in theirsize, and they are then introduced by means of a new current of airthrough the inlet into a third separating tower. The glass fragmentsdischarged from the coarse fraction outlet of this tower then undergo anafter-treatment and are finally collected in a waste container. Thefluorescent powder which is entrained in the currents of exhaust airfrom the outlets of the three separating towers is first separated offfrom this exhaust air by means of a cyclone, and thereafter by means ofdust filters. The mercury vapour which may possibly remain in theexhaust air thus filtered is finally separated off by means of charcoalfilters in order to prevent mercury vapour from reaching the atmosphere.

The larger material fragments separated off from the transportingcurrent of air in the separating towers can be discharged from thetowers, for example through the coarse fraction outlets at the bottomends of the towers, with the aid of a rotary valve which is arrangedthere.

The glass fragments which are separated off by the screening/sievingdownstream of the first separating tower, and the metal fragments whichare separated off in the second tower, can be transported past themagnetic separator on a common conveyor path, for example in the form ofa belt conveyor.

The after-treatment of the glass fragments discharged from the coarsefraction outlet of the third separating tower can be carried out, forexample for several minutes in a preferably ventilated, rotating drumfeeder or tumbler, from which the glass is then transported onwards bymeans of a discharging conveyor to the waste glass container.

To carry out the above-mentioned method, a system having the structuralelements specified in the system claims can preferably be used. A basicfeature of the system according to the invention is that the systemcomprises a preferably fan-driven exhaust air system which is designedfor the transport and separation of material fragments and particles andwhich is supplied with air from three separating towers which each havea material inlet, a coarse fraction outlet, and an air outlet which issituated at the uppermost part of the tower and which functions as afine fraction outlet. The mill responsible for the initial breaking-upof the discarded fluorescent light tube supplied to it can preferably bea hammer mill, the material outlet of which is then connected to thematerial inlet of the first tower.

The use of a hammer mill for initially breaking up the fluorescent lighttubes is preferable because a mill of this kind smashes or cracks thefluorescent light tubes into large pieces, which means that the metalend-sleeves with the lead oxide glass located therein remain relativelyintact. Most of the lead glass thus remains in the end-sleeves and isnot therefore mixed with the remainder of the glass.

The screen or the sieve which receives the discharged material from thecoarse fraction outlet of the first separating tower is used to dividethe material fragments thus discharged into glass fragments, on the onehand, and metal fragments, on the other hand, by means ofscreening/sieving. For further breaking up of these metal fragments, aspecial metal crusher is used whose material outlet is connected to theinlet of the second separating tower. Both the metal crusher and theglass crusher and the three separating towers can be of types which arealready known per se. The cyclone coupled between the air outlets of theseparating towers and the suction fan of the exhaust air system, withits downstream exhaust air filter, can also be of any suitable typewhich is already known. The fluorescent powder which is separated offfrom the air in the cyclone is expediently tapped off, via a bottomoutlet in the cyclone, straight down into a container for fluorescentpowder.

In one embodiment of the system which is particularly expedient from thepoint of view of environmental protection, the system is accommodatedentirely in a closed housing, preferably in the form of a closedstandard container, inside which a specific pressure is maintained whichis below the surrounding atmospheric pressure in the space or at thesite where the closed housing/container has been set up. The risk ofmercury or of mercury vapour being able to leak out into the surroundingenvironment outside the housing is in this way effectively avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described and explained in more detailhereinbelow, with reference to the attached drawings which show, on theone hand, the basic construction of a system according to the inventionand the flow of various fluorescent light tube materials through thesystem, and, on the other hand, an example of how the units included inthe system can be placed and grouped within a container housing whichaccommodates the system.

In the figures in the drawings:

FIG. 1 shows diagrammatically a system according to the invention, andmore specifically how the units included in the system are arranged tointeract with each other, the "flow arrows" showing the transport pathsof the fluorescent light tube material in the system, and how the air inthe system's fan-driven exhaust air system flows;

FIG. 2 shows, in a horizontal projection, the inside of a containerhousing which accommodates a commercial embodiment of a system accordingto the invention;

FIG. 3 shows, in a vertical projection, the system construction insidethe container housing according to FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made in the first instance to the system solutiondiagram in FIG. 1 in which the discarded fluorescent light tubes whichare to be treated in the system are fed, see arrow A, into a hammer mill2, preferably with the aid of a feed-in conveyor (not shown here). Thefluorescent light tubes which have been supplied are broken up intofragments in the mill 2, and these fragments are then suctioned out ofthe mill by means of a current of air 4 generated by the system'sfan-driven exhaust air system, which will be explained in more detail inthe description which follows. The fluorescent light tube fragmentswhich have thus been removed by suction from the mill 2 are introducedthrough an inlet 6 into a first vertically arranged separating tower 8.This tower has, at the bottom, a coarse fraction outlet 10 with a rotaryvalve 12 for discharging larger material fragments, of glass and metal,from the tower. These larger material fragments are separated off fromthe current of air in the separating tower, while smaller materialfragments and particles, such as fluorescent powder, are conveyedonwards by the air current and leave the tower through its air outlet 14which is located at the top and which functions as a fine fractionoutlet. As is evident from FIG. 1, the system comprises two furtherseparating towers 8' and 8" which also form part of the system and areconnected to the common exhaust air system, which is driven by a suctionfan 16. The air outlet 14 of each of the separating towers 8, 8', 8" areconnected to each other via air channels 18 and 20.

The larger fragments of material discharged from the tower 8 are thenmade to pass through a screen or a sieve 22 which divides them up intoglass fragments, which are conveyed onwards in accordance with the arrow24, and metal fragments, which are conveyed onwards in accordance withthe arrow 26 to a metal crusher 28. The term "screen" will be understoodhereinafter to mean both "screen" and "sieve", but for the sake ofclarity only the term "screen" will be used. In the same way, the term"screening" will be understood to mean both screening and sieving. Themetal fragments which have been supplied are crushed and broken up inthe crusher 28 into even smaller pieces, and these are then introduced,by means of a current of air 30, through the inlet 6 into the secondseparating tower 8'. The metal fragments which are separated off fromthe current of air in this second tower are then discharged through therotary valve 12 of the tower and are transferred to one half of a beltconveyor 32, on the other half of which the glass fragments from thescreen 22 are deposited, see arrow 24. Immediately above thematerial-transporting upper surface of the belt conveyor 32 there is amagnetic separator 34 which is arranged crosswise over the conveyor 32.The magnetic particles from the glass and metal paths of the conveyor,which particles have been separated off by means of the magneticseparator 34 from the upper surface of the belt conveyor 32, arecollected in a container (distiller barrel) 36 for possible furthertreatment, for example distillation. The fragments of metal, plastic,electrode and lead glass which have passed under the magnetic separator34 without being separated off are collected in a waste container 38 atthe end of the belt conveyor 32.

The glass fragments which have passed the separator 34 are then fed, seearrow 40, into a glass crusher 42 where they undergo a further reductionin their size. The glass which is now more finely divided is thenconveyed onwards from the glass crusher 42 by means of an air current 44in through the inlet 6 into the third separating tower 8". The glasswhich is separated off from the air current in the separating tower 8"and is discharged from the tower via the rotary valve 12 is thereaftertransferred to a conveyor 46 which feeds the glass, see arrow 48, to theinlet end of a drum feeder 50 inside which the glass undergoes a finalafter-treatment for a few minutes. From the outlet end of the drumfeeder 50, the glass is transferred to a belt conveyor 52 from which theglass is finally delivered, see arrow B, to a waste container 54.

The airborne material which has been emitted through the air channel 56from the outlets 14 of the separating towers 8, 8' and 8", and whichessentially consists of fluorescent powder, is conveyed onwards into theupper end of a cyclone 58, where most of the fluorescent powder isseparated off from the current of air and discharged via a bottom outlet60, see arrow C, to a waste container 62 for fluorescent powder. The aircleaned in the cyclone 58 then continues through the channel 64 to adust filter 66 where the finer particles in the air are also separatedoff and delivered to a container (distiller barrel). From the dustfilter 66, the exhaust air is conveyed onwards through the channel 68 toa battery of charcoal filters 70. In these charcoal filters, anyremaining mercury vapour is finally separated off from the current ofair which is led from the charcoal filters, via a channel 72, to theintake side of the fan 16. In the case of a completely closed exhaustair system, the cleaned air which has now reached the fan 16 can then beled, from the pressurized delivery side (not shown) of the fan, back tothe flow path 4 downstream of the hammer mill 2.

As has been pointed out above, FIG. 1 shows the basic construction of asystem according to the invention, i.e. how the units included in thesystem are designed to interact with each other. In practice, the systemis of course designed in such a way that both the air transportationpaths and the conveyor paths of the various belt conveyor are notunnecessarily long and do not take up too much space. It is thereforedesirable that the whole system be designed in such a way that the unitsincluded (mill, separating towers, crushers, screen, conveyors, magneticseparator, rotary drum feeder, cyclone, filters and fan) are grouped inan optimal manner from the point of view of system construction andadditionally in such a way that they are accessible for inspection andmaintenance.

From the point of view of environmental protection, it is also desirablethat the whole system can be accommodated in a closed housing in whichit is possible to maintain a specific subatmospheric pressure whichprevents mercury or mercury vapour leaking out from the system and intothe surrounding atmosphere.

For the abovementioned reasons, it is expedient that the system be givena commercial design which is more compact than that shown in FIG. 1.

Such a commercial design in which the system is accommodated in a closedhousing unit, for example a 20-foot standard container 74, is shown inFIGS. 2 and 3. This commercial construction of the system correspondsentirely with the basic construction which is shown in FIG. 1, the onlydifference being that the units included in the system have been placedin an optimal manner from the point of view of function and systemconstruction. Since FIGS. 2 and 3 therefore concern units which are thesame as those in accordance with the basic embodiment in FIG. 1, thereis no need here for a renewed explanation of the construction of thesystem and its function, and instead reference is made quite simply toFIGS. 2 and 3 where the units have been provided with the same referencelabels as in FIG. 1.

We claim:
 1. Method for mechanical separation of various materials fromdischarged fluorescent light tubes and similar low-pressure dischargelamps being broken up, which comprises:feeding discarded fluorescentlight tubes into a mill where they are broken up into materialfragments; introducing the material fragments with a current of air intoa first separating tower where larger material fragments, of glass andmetal, are separated off from the current of air and are discharged fromthe tower, while smaller material fragments and particles, includingfluorescent powder, are conveyed onwards by the current of air; dividingthe larger material fragments which have been discharged from the towerinto glass fragments and metal fragments by screening; conveying theglass fragments onwards past a magnetic separator; feeding the metalfragments into a crusher to obtain crushed metal fragments; introducingthe crushed metal fragments with a current of air into a secondseparating tower from which they are transported onwards past themagnetic separator; collecting the magnetic material fragments whichhave been separated off by the magnetic separator in a container;feeding the glass fragments which have passed the magnetic separatorinto a glass crusher, where they undergo further reduction in size;introducing the glass fragments of reduced size with a current of airinto a third separating tower, from which they are discharged;collecting the glass fragments discharged from the third separatingtower in a waste glass container; separating off fluorescent powderentrained in the currents of exhaust air from the separating towers bypassing said currents of exhaust air first through a cyclone, andthereafter through a dust filter; and thereafter separating off anyremaining mercury vapor in the exhaust air by passage through charcoalfilters.
 2. The method according to claim 1, wherein the larger materialfragments which have been separated off from each tower's incomingcurrent of air are discharged from the respective separating towerthrough a rotary valve which is arranged at the bottom end of therespective separating tower.
 3. The method according to claim 1, whereinat least a greater part of airborne particulate material, including thefluorescent powder, which is introduced with the current of air intoeach separating tower is conveyed further upwards through the tower bythe current of air and leaves an upper end of the tower together withthe current of air issuing from the tower.
 4. The method according toclaim 1, wherein the glass fragments which have been separated off byscreening downstream of the first separating tower, and the metalfragments which have been separated off in the second separating tower,are transported past the magnetic separator on a common conveyor path.5. The method according to claim 1, wherein the glass fragmentsdischarged from the third separating tower are after-treated for a fewminutes in a rotating ventilating drum feeder, from which they are thentransported to the waste glass container via a discharging conveyor. 6.System for mechanical separation of various materials from discardedfluorescent light tubes and similar low-pressure discharge lamps beingbroken up, the system comprising:a fan-driven exhaust air systemstructured and arranged to transport and separate material fragments andparticles, said exhaust air system being supplied with air from threeseparating towers which are each provided with an inlet, a coarsefraction outlet, and an air outlet functioning as a fine fractionoutlet; a mill for breaking up the discarded fluorescent light tubes,said mill having an outlet connected to the inlet of the firstseparating tower in which larger material fragments are separated offfrom the current of air which transports broken-up material from themill to the first separating tower, while smaller material fragments andparticles are carried off from the air outlet of the first separatingtower, together with the current of air, to the exhaust air system; ascreen for dividing the material fragments discharged from the coarsefraction outlet of the first separating tower into glass fragments andmetal fragments; a metal crusher structured and arranged between thescreen and the second separating tower for further breaking-up the metalfragments supplied from the screen; the inlet of the second separatingtower being connected to an outlet of the metal crusher; a magneticseparator arranged between the screen and the coarse fraction outlet ofthe second separating tower, and a glass crusher whose outlet isconnected to the third separating tower; a waste glass containerarranged to receive glass fragments from the coarse fraction outlet ofthe third separating tower; and a cyclone with downstream exhaust airfilters coupled between the air outlets of the separating towers and asuction fan of the exhaust air system.
 7. The system according to claim6, further comprising a belt conveyor receiving glass fragments from thescreen and metal fragments from the coarse fraction outlet of the secondseparating tower, said belt conveyor extending past the magneticseparator so that magnetic material on the moving belt surface of theconveyor is removed by the magnetic separator, said belt conveyor havinga downstream end arranged to deliver glass fragments to the glasscrusher and metal fragments to a waste metal container.
 8. The systemaccording to claim 6, further comprising a conveyor path fortransporting glass fragments from the coarse fraction outlet of thethird separating tower to the waste glass container, said conveyor pathcomprising, in succession, a belt conveyor, a drum feeder which receivesmaterial from a discharge end of the belt conveyor, and a dischargingconveyor which receives material from a discharge end of the drum feederand which delivers the material to the waste glass container.
 9. Thesystem according to claim 6, wherein each separating tower has, as itscoarse fraction outlet, a rotary valve which is arranged in thelowermost part of the tower and which is used for discharging the largermaterial fragments which have been separated off from incoming currentof air in the tower.
 10. The system according to claim 6, wherein themill is a hammer mill which smashes the supplied fluorescent tubes intofairly large bits.
 11. The system according to claim 6, wherein theentire system is accommodated in a closed housing in the form of aclosed 20-foot container, which includes means for maintaining thespecific pressure therein which is below the surrounding atmosphericpressure at the site of the housing.